Optical reader stations for scanning symbols have applications such as inventory control, parcel tracking, identification and security, i.e. wherever an electronic database may be maintained against a set of tangible elements. In such a station, the symbology reader performs the necessary function of converting the tangible information into electronic information.
Scanners in the optical reader stations may be handheld, permanently mounted, or they may consist of handheld scanners with a complementary mount for use in presentation mode scanning. In particular situations such as grocery checkouts or identification queues, a scanner is preferably a fixed mount or in a presentation mode of operation. In general, it is desirable that such stations draw low power, operate under low component stress, are simple and cost-effective to manufacture, are unobtrusive in their deployment, and are retrofitable and make use of existing system resources when improvements are considered.
Each symbology reader has imaging and decoding functions. The imaging function acquires an image of a coded object and converts the optical image information to corresponding electronic information. The decoding function extracts the encoded message from the electronic information.
The reader may also include other major functions where necessary or advantageous. For example a reader may include the functions of illuminating and/or targeting the symbol to be read. Variable illumination may be required to supply sufficient photonic radiation to capture a suitable image in varying ambient conditions. The required level of illumination on the object may be controlled by an auto-exposure function within the reader. A targeting system aids in positioning the symbol in the field of view.
Different strategies have been used during the development of readers. Some reader systems have inactive and active states, wherein they are activated to scan an object in response to an event, such as the pressing of a button, after which they return to their inactive state. The event that activates this type of reader might also be the detection of the absence or presence of a predetermined symbology in the object field by periodically scanning it. The absence of the predetermined symbology may signify that a valid object has been placed in the object field. Other types of readers are always active once they are switched on in that they continuously scan the object field and attempt to decode the imaged information without regard to the presence of a valid symbol within the field.
One method for controlling the active/inactive states of a reader is described in U.S. Pat. No. 5,949,052, which issued to Longacre, Jr. et al on Sep. 7, 1999. This disclosure is directed to the use of a special default symbol, the detection of which places the reader in an active state. This device may employ a predetermined pattern of backlighting on the surface where an object is to be placed. The backlighting lights a predetermined symbol from the back, which is scanned periodically and decoded by the reader. When the predetermined symbol is detected, the reader is placed in an inactive mode, when the predetermined symbol is not detected and the reader is placed in an active mode. When the predetermined symbol is not detected, it means that an object to be read is obstructing the line of sight from predetemined symbol to the reader, and the reader is activated to operate in its normal operating mode. Another form that the backlighting technique may take is described in U.S. Pat. No. 6,298,175, which issued to Longacre, Jr. et al on Oct. 2, 2001, wherein the backlighting emits light in a predetermined pattern such as being intermittently on and off, which is recognized by the reader. Although this solution provides benefits such as power saving, a station must be modified to include new apparatus and programming to both generate and recognize the predetermined symbol, or pattern. Another drawback is the latency introduced by this approach arising from the duration of switching to an active state. Increased latency lowers station productivity.
Existing continuous scan configurations do not adequately conserve power, and often operate with a constant or pulsed illumination source, which is found to be obtrusively non-ergonomic. In addition, the systems described above are not satisfactory solutions for existing event driven or continuous configurations. They do not provide a sufficiently simple low latency, cost-effective option that minimizes the use of new resources by maximizing the incorporation with existing reader resources, making it retrofittable in a simple manner.
Therefore, there is a need for improved unobstusive optical reader stations, with minimal user interaction, low latency and low energy use.